Golf ball

ABSTRACT

A golf ball of the present invention includes: a core located in the center of the golf ball; a cover which surrounds the outside of the core and has a plurality of dimples on the surface thereof; and a coating layer located between the core and the cover. The coating layer is formed of a material having rubber elasticity. The μ hardness of the golf ball is preferred to be approximately 3.0 or more and the cover is preferred to have a hardness of approximately 50 or more in terms of Shore D hardness. The intermediate layer is preferred to have a hardness of approximately 40 to approximately 65 in terms of Shore D hardness, and the hardness of the cover is preferred to be higher than the hardness of the intermediate layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention claims the benefits of U.S. patent application Ser. No. 13/328,506 filed Dec. 16, 2011, U.S. patent application Ser. No. 13/409,994 filed Mar. 1, 2012, and U.S. patent application Ser. No. 13/410,012 filed Mar. 1, 2012.

BACKGROUND OF THE INVENTION

The present invention relates to a golf ball, and more particularly, relates to a golf ball containing a soft coating layer internally.

Usually, the surface of the golf ball is provided with a coating layer. The coating layer is demanded to have performances in appearance such as color tone, impact resistance and abrasion resistance. Japanese Patent Application Publication No. 8-206255 has disclosed a golf ball having a coating layer formed of coating material composition including acrylic polyol, polyester polyol and hardening agent in order to improve its impact resistance and abrasion resistance.

A high-performance golf ball has a small spin amount when it is hit with a driver, thereby increasing a flying distance. When the ball is hit for approach, its spin amount is increased to secure an excellent controllability around the green. To improve the above-described performance, Japanese Patent Application Publication No. 9-276446 has disclosed an idea that by using two coating layers, an inside layer is formed as a white coating film of thermoplastic resin by dispersion coating, and the outside layer is formed of transparent coating film of thermoplastic resin by dispersion coating.

Furthermore, Japanese Patent Application Publication No. 2001-000585 has disclosed a golf ball having an adhesive layer formed of epoxy resin adhesive, urethane resin adhesive, vinyl resin adhesive or rubber adhesive, between an intermediate layer and a cover. This publication has stated that the golf ball having such adhesive layer ensures a high resilience property and the spin performance in an iron shot is excellent.

Japanese Patent Application Publication No. 11-137725 has disclosed a golf ball in which of its intermediate layer and cover, one is formed of ionomer resin and the other is formed of urethane resin and that an adhesive layer is formed between the inside layer cover and the outside layer cover. This publication stated that the golf ball having such a configuration has resistance to repeated impacts and that it has a large spin amount when hit for approach while the spin amount in a driver shot is small.

SUMMARY OF THE INVENTION

An object of the present invention is to improve the above-described conventional technologies and provide a golf ball capable of increasing the spin amount when hit with a driver while holding the spin amount when hit for approach, this golf ball ensuring an excellent durability.

The golf ball of the present invention includes: a core located in the center of the golf ball; a cover which surrounds the outside of the core and has a plurality of dimples on the surface thereof; and a coating layer located between the core and the cover, the coating layer being formed of a material having rubber elasticity. The golf ball of the present invention may further include an intermediate layer located between the core and the cover and the coating layer is located between the core and the intermediate layer or between the intermediate layer and the cover. According to a simulation performed by the inventor of the present invention, it has been found that provision of the coating layer having rubber elasticity inside of the golf ball allows the spin amount when the ball is hit with a driver to be increased while maintaining the spin amount upon an approach shot on a current level.

Generally, a golfer having a low head speed tends to apply a low spin to the golf ball when it is hit with a driver so that flight distance may be lost. The golfer having such a low head speed tends to like soft balls. However, because the soft ball is structured not to spin well when it is hit by an approach shot, the ball is not spun even when it is hit with a driver. A μ hardness of the ball of approximately 3.0 or more is in a range which makes the ball to be spun low when it is hit with a driver, and amateur golfers like such a hardness range. A ball of which Shore D hardness is approximately 50 or more is structured to be spun low when it is hit with a driver. However, golfers who wish to roll a ball upon an approach shot like such a ball. Even the golf ball having such a hardness is capable of increasing the spin amount when it is hit with a driver by providing the coating layer of material having rubber elasticity inside of the ball.

If any intermediate layer is provided, preferably, the intermediate layer has a hardness of approximately 40 to 65 in terms of Shore D hardness and the hardness of the cover is higher than the hardness of the intermediate layer. Usually, although the durability of the golf ball is determined by its cover, provision of the coating layer having a low hardness and additionally the intermediate layer under the cover relaxes a shock on the cover thereby leading to improvement of the durability.

The coating layer may have a thickness of approximately 10 to approximately 150 μm. The material for forming the coating layer may have a Young's modulus of approximately 70 MPa. The material for forming the coating layer may have a Poisson's ratio of approximately 0.45 or more. The coating layer may have a hardness of approximately 70 or less in terms of JIS-C hardness. The cover may contain ionomer resin.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan sectional view showing an embodiment of a golf ball according to the present invention.

FIG. 2 is a plan sectional view showing another embodiment of the golf ball according to the present invention.

FIG. 3 is a plan sectional view showing still another embodiment of the golf ball according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of a golf ball according to the present invention will be described with reference to the accompanying drawings. However, the present invention is not restricted to these embodiments. In the meantime, the accompanying drawings are drawn mainly to facilitate understanding of the present invention, but they are not drawn to scale.

As shown in FIG. 1, the golf ball 1 of the present embodiment mainly includes a core 10 located in the center of the ball, a cover 30 surrounding the outside of the core and a coating layer 40 located between the core and the cover. Plural dimples 32 are formed on the surface of the cover 30. The coating layer 40 covers the surface of the core 10 with a substantially equal thickness.

In addition, the golf ball of the present invention is not limited to the structure shown in FIG. 1, but may be as shown in FIG. 2 or 3, it may have arbitrary freely chosen intermediate layer 20 between the cover 10 and the cover 30. Although in FIG. 1, the coating layer 40 is formed to make direct contact with both the core 10 and the cover 30, the coating layer 40 may be formed between the core 10 and the intermediate layer 20 as shown in FIG. 2, or between the intermediate layer 20 and the cover 30, as shown in FIG. 3.

The core 10 may be formed mainly of base rubber. As the base rubber, a variety of rubbers (thermoplastic elastomer) may be used, such as polybutadiene rubber (BR), styrene-butadiene rubber (SBR), natural rubber (NR), polyisoprene rubber (IR), polyurethane rubber (PU), butyl rubber (IIR), vinyl polybutadiene rubber (VBR), ethylene-propylene rubber (EPDM), nitrile rubber (NBR), silicone rubber; however the present invention is not restricted to these materials. As the polybutadiene rubber (BR), for example, 1,2-polybutadiene, cis-1,4-polybutadiene and the like may be used.

As well as the base rubber which is a main component, for example, co-cross linking agent, cross linking agent, filler, age resistor, isomerization agent, peptizing agent, sulfur and organic sulfur compound may be added to the core 10. As the main component, thermoplastic elastomer, ionomer resin or a mixture of these components may be used instead of the base rubber.

As the co-cross linking agent, it is preferable to use, for example, α,β-unsaturated carboxylic acid or its metallic salt, although it is not restricted to these materials. As the α,β-unsaturated carboxylic acid or its metallic salt, for example, acrylic acid, methacrylic acid, and zinc salt, magnesium salt and calcium salt of these substances are available. Although the composition of the co-cross-linking agent is not limited to this example, for example, assuming that the base rubber is 100 parts by weight, it is preferred to be approximately 5 parts or more by weight and is more preferred to be approximately 10 parts or more by weight. Furthermore, the composition of the co-cross-linking agent is preferred to be approximately 70 parts or less by weight and is more preferred to be approximately 50 parts or less by weight.

As the cross-linking agent, it is preferred to use an organic peroxide, although this is not restricted to this substance. Assuming that the base rubber is 100 parts by weight, the composition of an initiator is preferred to be approximately 0.10 parts by weight, is more preferred to be approximately 0.15 parts by weight, and is further preferred to be approximately 0.30 parts by weight, although it is not restricted to these values. The composition of the initiator is preferred to be approximately 8 parts or less by weight and is more preferred to be approximately 6 parts or less by weight.

Although, as the filler, for example, silver, gold, cobalt, chrome, copper, germanium, manganese, molybdenum, nickel, lead, platinum, tin, titanium, tungsten, zinc, zirconium, barium sulfate, zinc oxide, and manganese oxide may be used, it is not restricted to these substances. The filler is preferred to be in a form of powder. Assuming that the base rubber is 100 parts by weight, the composition of the filler is preferred to be approximately 1 part or more by weight, is more preferred to be approximately 2 parts or more by weight and is further preferred to be approximately 3 parts or more by weight. Furthermore, the composition of the filler is preferred to be approximately 100 parts or less by weight, is more preferred to be approximately 80 parts or less by weight, and is further preferred to be approximately 70 parts or less by weight.

The core 10 is substantially spherical. The outside diameter of the core 10 is preferred to be approximately 42 mm or less, is more preferred to be approximately 41 mm or less, and is further preferred to be approximately 40 mm or less. Because if the outside diameter of the core is too small, the resiliency of the golf ball is decreased, it is preferred to be approximately 5 mm or more, is more preferred to be approximately 15 mm or more, and is further preferred to be approximately 25 mm or more. Although the core 10 shown in FIG. 1 is solid, the core is not restricted to this example, but may be hollow. Although the core 10 shown in FIG. 1 is of a single layer, the core is not restricted to this example, but may be constituted of plural layers, which may include, for example, a center core and surrounding layers.

As the forming method of the core 10, any known forming method for the core of the golf ball may be adopted. For example, the core may be obtained by kneading materials including the base rubber with a kneading machine and vulcanizing the kneaded materials under a pressure with a round mold. As a method for forming a core having plural layers, it is permissible to adopt a known forming method for the multi-layered solid-core. For example, materials are kneaded with the kneading machine and then, the center core is obtained by vulcanizing the kneaded materials under a pressure with a round mold. After that, for the surrounding layers, again, materials are kneaded with the kneading machine and the kneaded materials are formed into a sheet. Then, the center core is covered with this sheet and vulcanized under a pressure with the round mold to obtain a multi-layered core.

The cover 30 may be formed using ionomer resin, polyurethane thermoplastic elastomer, thermoplastic polyurethane or a mixture of these substances although the material thereof is not restricted thereto. Furthermore, as well as the aforementioned ionomer resin, polyurethane thermoplastic elastomer, and thermoplastic polyurethane which serve as a main component, other thermoplastic elastomer, polyisocyanate compound, fatty acid or its derivative, basic inorganic metal compound or filler may be added to the cover 30.

As the ionomer resin, following resins containing a component (a) and/or a component (b) may be used as base resin, although it is not restricted to these substances. Furthermore, a following component (c) may be added to this base resin freely. The component (a) is olefin-unsaturated carboxylic acid-unsaturated carboxylic ester random terpolymer and/or its metallic salt. The component (b) is olefin-unsaturated carboxylic acid random copolymer and/or its metallic salt. The component (c) is thermoplastic block copolymer having polyolefin crystalline block and polyethylene/butylene random copolymer.

The thickness of the cover 30 is preferred to be approximately 0.2 mm or more, and is more preferred to be approximately 0.4 mm or more, although it is not restricted to these values. Furthermore, the thickness of the cover 30 is preferred to be approximately 4 mm or less, is more preferred to be approximately 3 mm or less and is further preferred to be approximately 2 mm or less. Plural dimples 32 are formed on the surface of the cover 30. The size, shape and quantity of the dimples 30 may be designed appropriately corresponding to a desired aerodynamic characteristic of the golf ball 1.

The hardness of the cover 30 is preferred to be approximately 50 or more in terms of Shore D hardness, and is more preferred to be approximately 55, although it is not restricted to this example. Additionally, the hardness of the cover 30 is preferred to be approximately 75 or less, is more preferred to be approximately 70 or less and is further preferred to be approximately 65 or less.

To form the cover 30, any known forming method for the cover of the golf ball may be adopted. For example, the cover 30 is formed by injection-molding a material for the cover into a mold, although the forming method is not restricted to any particular one. The mold for forming the cover has cavities for molding the cover, and this cavity has plural projections for forming the dimples on the wall surface thereof. By disposing the core 10 in the center of the cavity, the cover 30 is formed such that it surrounds the core 10.

The coating layer 40 is formed of a material having rubber elasticity. The Young's modulus of the material having rubber elasticity is preferred to be approximately 0.1 MPa or more, is more preferred to be approximately 1 MPa or more, and is further preferred to be approximately 3 MPa or more, although the material for use is not restricted to these materials. Furthermore, the Young's modulus of the material is preferred to be approximately 70 MPa or less, is more preferred to be approximately 65 MPa or less, and is further preferred to be approximately 60 MPa or less. The Poisson's ratio of the material having rubber elasticity is preferred to be approximately 0.45 or more, is more preferred to be approximately 0.46 or more and is further preferred to be approximately 0.47 or more, although the material for use is not restricted to these materials. Furthermore, the Poisson's ratio of the material is preferred to be approximately 0.60 or less, is more preferred to be approximately 0.55 or less, and is further preferred to be approximately 0.50 or less. Unless the Young's modulus and the Poisson's ratio are within the above-mentioned ranges, a coating layer 40 may not ensure a sufficient plasticity or friction force.

Regarding a material having such rubber elasticity, according to, for example, a classification of JIS K6397, as an M-group (rubbers having polymethylene type saturated main chain), ACM (acrylic rubber or rubber-like copolymer formed of ethyl acrylate or other acrylic ester with a small amount of monomer allowing vulcanization), AEM (rubber-like copolymer formed of ethyl acrylate or acrylic ester with ethylene), ANM (rubber-like copolymer formed of ethyl acrylate or acrylic ester with acrylonitrile), CM (polyethylene chloride), CSM (chlorosulfonated polyethylene, trade name: Hypalon), EPDM (rubber-like copolymer formed of ethylene, propylene and diene. Called EPT also), EPM (rubber-like copolymer formed of ethylene and propylene. Called EPR also), and EVM (rubber-like copolymer formed of ethylene and vinyl acetate) polymers may be used.

As an O group (rubber having carbon and oxygen as main chain), polymers such as CO (called epichlorohydrin rubber or polychloromethyl oxirane also) and ECO (rubber-like copolymer formed of ethylene oxide and Epichlorohydrin) may be used.

As an R group (rubber having unsaturated carbon bonds in the main chain), BR (butadiene rubber), CR (chloroprene rubber, Trade name: neoprene), IIR (butyl rubber or rubber-like copolymer formed of isobutene and isoprene), IR (synthetic natural rubber or isoprene rubber), NBR (nitrile rubber or rubber-like copolymer formed of acrylonitril and butadiene), NR (natural rubber), NOR (polynorbornene rubber), SBR (rubber-like copolymer formed of styrene and butadiene), E-SBR (rubber-like copolymer formed of styrene and butadiene by emulsion polymerization), S-SBR (rubber-like copolymer formed of styrene and butadiene by solution polymerization), SIBR (rubber-like copolymer formed of styrene, isoprene and butadiene), XBR (carboxylated butadiene rubber), XCR (carboxylated chloroprene rubber), XNBR (carboxylated rubber-like copolymer formed of acrylonitril and butadiene), XSBR (carboxylated rubber-like copolymer formed of styrene and butadiene), BIIR (brominated butyl rubber or rubber-like copolymer formed of brominated isobutene and isoprene), CIIR (chlorinated butyl rubber or rubber-like copolymer formed of chlorinated isobutene and isoprene) may be used.

The thickness of the coating layer 40 is preferred to be approximately 10 μm or more and more preferred to be approximately 30 μm or more, and is further preferred to be approximately 50 μm or more, although it is not always restricted to these values. Furthermore, the thickness of the coating layer 40 is preferred to be approximately 150 μm or less and is more preferred to be approximately 120 μm or less, and is further preferred to be approximately 100 μm. If the thickness of the coating layer is too small, the spin amount upon a driver shot cannot be increased sufficiently. If the thickness of the coating layer is too great, the durability of the golf ball sometimes can decline.

The hardness of the coating layer 40 is preferred to be approximately 10 or more in terms of JIS-C hardness, is more preferred to be approximately 20 or more, and is further preferred to be approximately 30 or more, although it is not restricted to these values. Furthermore, the hardness of the coating layer 40 is preferred to be approximately 70 or less, is more preferred to be approximately 60 or less, and is further preferred to be approximately 50 or less. In particular, the hardness of the coating layer 40 is preferred to be lower than that of the core 10. Furthermore, the core 10 may be formed such that its hardness is increased gradually from the center of the core to the surface of the core. By forming a golf ball so that the hardness thereof increases gradually from the core center toward the surface, the driver spin can be reduced to increase the flying distance. Here, the hardness of the coating layer 40 is preferred to be lower than the hardness of the center of the core and more preferred to be lower by approximately 10 or more. If the hardness of the coating layer 40 is higher than the hardness of the center of the core, no appropriate spin may be obtained.

The μ hardness of a golf ball product 1 is preferred to be approximately 3.0 or more, more preferred to be approximately 3.2 or more, and is further preferred to be approximately 3.5 or more. The upper limit thereof is preferred to be approximately 5.0 or less and is more preferred to be approximately 4.5 or less. The μ hardness of the product refers to an amount of deflection (deformation) when the golf ball product 1 is loaded with an initial load of 98 N (10 kgf) up to 1,275 N (130 kgf) while the unit is expressed in mm. If the μ hardness of the product is increased too much, an amateur golfer's feeling upon hitting the golf ball becomes too stiff, which may be undesirable.

As a formation method for the coating layer 40, any known formation method for the coating layer of the golf ball may be adopted even if the coating layer 40 is formed on the surface of the core 10 or the intermediate layer 20. For example, for the coating layer 40, a liquid coating material can be obtained by diluting material having the above-described rubber elasticity with solvent, although it is not restricted to any particular material. As the solvent, n-pentane, gasoline, n-hexane, diethyl ether, cyclohexane, isobutyl acetate, butyl acetate, isopropyl acetate, methyl isopropyl ketone, xylene tetrachloride, methyl propyl ketone, ethyl benzene, xylene, toluene, ethyl acetate, tetrahydrofuran, benzene, chloroform, methyl ethyl ketone, trichloroethylene, acetone, n-hexanol and the like may be used, although this is not restricted to any particular type. The dilution rate (concentration of coating polymer) may be approximately 5% to approximately 100% although this is not restricted to any particular value.

After coating the surface of the core 10 or the intermediate layer 20 with this coating material, the coating layer 40 may be formed by a cross-linking process. The coating method is not restricted to any particular one, but any coating material may be applied by a spraying method, dipping method, rolling method or spin method. Although the cross-linking method is not restricted to any particular type, it is preferable to add a cross-linking agent or a hardening agent to the above-mentioned coating material, so that, after the coating material is applied, cross-linking or hardening is induced. As the cross-linking agent or the hardening agent, cross-linking with, for example, peroxide, metal, amine, oxime, resin, or sulfur is preferable to obtain the coating layer 40 having a sufficient impact resilience. Furthermore, as well as the cross-linking agent and the hardening agent, a filler may be freely added to the coating material. Even material difficult to cross-link may be applied by dispersing the material having a long molecular chain in solvent, and even if no cross-linking agent is used, the molecular chains tangle with each other to produce coating material having rubber elasticity.

A top coat (not shown) may be freely formed on the cover 30. As the top coat material, any known material suitable for the top coat of the golf ball may be used. As the material, polyester polyol or acrylic polyol may be used and fixed with a hardening agent. For example, two-liquid type curable urethane coating material may be mentioned, and particularly, it is preferable to use a non-yellowing type coating material. The thickness of the top coat is preferred to be, for example, approximately 5 μm or more and is more preferred to be approximately 10 μm or more. Furthermore, the thickness of the top coat is preferred to be approximately 100 μm or less and is more preferred to be approximately 60 μm or less.

The intermediate layer 20 disposed between the core 10 and the cover 30 is not indispensable, but it may be freely provided. It is permissible to provide an intermediate layer which functions as a core or a cover. Furthermore, it is also permissible to provide plural intermediate layers, for example, plural intermediate layers which function as the core or the cover, or a first intermediate layer that functions as the core with a second intermediate layer that functions as the cover.

For materials of the intermediate layer 20, the following heated mixture is preferably used, as the main material, but the materials are not limited thereto. Using the following mixture for the intermediate layer can lower the spin rate of the hit ball, and thus, long distance can be achieved.

(a) at least one of olefin-unsaturated carboxylic acid random copolymer and a metal ion neutralizing material of olefin-unsaturated carboxylic acid random copolymer, (b) at least one of olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester random terpolymer and a metal ion neutralizing material of olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester random terpolymer, (c) at least one of fatty acid having a molecular weight of 228 to 1500 and its derivative, (d) basic inorganic metallic compound capable of neutralizing an unneutralized acid group in components (a) to (c), and (e) non-ionomer thermoplastic elastomer, wherein a base resin contains component (a) and component (b) which are mixed in a ratio of 100:0 to 0:100 by weight, wherein the base resin and component (e) are mixed in a ratio of 100:0 to 50:50 by weight, and wherein 5 to 150 parts by weight of component (c) and 0.1 to 17 parts by weight of component (d) are added to the resin component containing the base resin and component (e) with respect to 100 parts by weight of the resin component.

The “main material” mentioned here means a material which has approximately 50 weight % or more with respect to the total weight of the intermediate layer 20, preferably approximately 60 weight % or more and more preferably approximately 70 weight % or more.

The hardness of the intermediate layer 20 is preferred to be approximately 40 or more in terms of Shore D hardness, more preferred to be approximately 45 or more and is further preferred to be approximately 50 or more. The hardness of the intermediate layer 20 is preferred to be lower than the hardness of the cover 30, and is particularly preferred to be approximately 65 or less in terms of Shore D hardness and is more preferred to be approximately 60 or less.

The thickness of the intermediate layer 20 is preferred to be approximately 0.5 mm or more and is more preferred to be approximately 1 mm or more, although it is not restricted to these values. Furthermore, the thickness of the intermediate layer 20 is preferred to be approximately 10 mm or less, is more preferred to be approximately 5 mm or less and is further preferred to be approximately 3 mm or less. Although the intermediate layer 20 is represented in a single layer in FIG. 1, it is not limited to this example and it may be of plural layers, i.e., two layers or more.

Example

Golf balls having each configuration shown in Table 1 were manufactured, and then tests for measuring the spin performance of each golf ball were performed. In each test case, five balls were prepared and evaluated. Table 1 shows a test result indicating each average of the five balls. Table 2 shows compositions A1 and A2 of the core material shown in Table 1 (in parts by weight). Table 3 shows compositions B to D of the cover and intermediate layer materials (in parts by weight). Table 4 shows a composition E of the coating layer material (in parts by weight). In the meantime, the coating layer was formed by diluting a material having a predetermined composition by 30% to 50% using toluene and spraying the diluted material.

TABLE 1 Example Comparative example 1 2 3 4 5 6 7 8 1 2 3 Core Outside diameter (mm) 37.1 37.1 37.3 37.1 37.1 37.3 37.1 37.1 37.3 37.3 37.1 Composition A1 A2 A2 A1 A2 A2 A2 A2 A1 A2 A2 Coating layer Thickness (μm) — — — 100 100 20 — 100 — — — Young's modulus (MPa) — — — 12 12 12 — 12 — — — Composition — — — E E E — E — — — Intermediate Thickness (mm) 1.45 1.45 1.45 1.45 1.45 1.45 1.45 1.45 1.45 1.45 1.45 layer Shore D hardness 51 51 51 51 51 51 51 51 51 51 51 Composition D D D D D D D D D D D Coating layer Thickness (μm) 100 100 20 — — — 100 — — — — Young's modulus (MPa) 12 12 12 — — — 12 — — — — Composition E E E — — — E — — — — Cover Thickness (mm) 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25 Shore D hardness 63 63 63 63 63 63 58 58 63 63 58 Composition B B B B B B C C B B C Product μ hardness 3.1 4.0 4.0 3.1 4.0 4.0 4.2 4.2 3.1 4.0 4.2 Spin Driver 2220 2130 2080 2210 2110 2150 2420 2410 2080 1970 2300 performance Approach 4400 4600 4600 4400 4600 4600 5200 5200 4400 4600 5200 COR durability (times) 160 135 140 115 115 120 210 190 140 100 180

TABLE 2 Composition of core A1 A2 Polybutadiene 100 100 Zinc acrylate 21.0 15.0 Peroxide 1 0.6 0.6 Peroxide 2 0.6 0.6 Anti-aging agent 0.1 0.1 Zinc oxide 30.0 32.3 Core hardness Center (JIS-C) 58 53 Surface (JIS-C) 72 65 Vulcanization Temperature (C. °) 155 155 method Time (h) 15 15

As polybutadiene, BR01 manufactured by JSR was used as base rubber. As zinc acrylate, WN86 manufactured by Nippon Shokubai was used. As peroxide 1, dicumylperoxide manufactured by NOF Corporation was used, the product name of which is Percumyl D. As peroxide 2, a mixture of 1,1 di(t-butylperoxy) cyclohexane and silica, manufactured by NOF was used, the product name of which is Perhexa C-40. This product was used as an initiator. As anti-aging agent, 2,2′-methylenebis(4-methyl-6-t-butylphenol), manufactured by Ouchi Shinko Kagaku was used, the product name of which is Nocrac NS-6. As zinc oxide, a product manufactured by Sakai Kagaku Kogyo was used, the product name of which is Zinc Oxide Grade 3.

TABLE 3 Composition of cover B C D Himilan 1557 — 42.5 — Himilan 1605 40 — — Himilan 1706 50 — — Himilan 1601 10 42.5 — AN4318 — 15 AN4319 — — 100 Magnesium stearate — — 70 Magnesium oxide — — 1.9 TiO₂ 3 3 — Blue 0.04 0.04 —

Himilan 1557 is an ionomer resin of Zn-ion neutralizing ethylene-methacrylate copolymer manufactured by Mitsui DuPont Chemical.

Himilan 1605 is an ionomer resin of Na-ion neutralizing ethylene-methacrylate copolymer manufactured by Mitsui DuPont Chemical. Himilan 1706 is an ionomer resin of Zn-ion neutralizing ethylene-methacrylate copolymer manufactured by Mitsui DuPont Chemical. Himilan 1601 is an ionomer resin of Na-ion neutralizing ethylene-methacrylate copolymer manufactured by Mitsui DuPont Chemical. AN4318 is olefin-unsaturated carboxylic acid-unsaturated carboxylic ester terpolymer manufactured by Mitsui DuPont Chemical. AN4319 is olefin-unsaturated carboxylic acid-unsaturated carboxylic ester terpolymer manufactured by Mitsui DuPont Chemical. TiO₂ is Taipak R550 manufactured by ISHIHARA SANGYO KAISHA LTD. Blue is a product EP-62 manufactured by Holiday Pigments.

TABLE 4 Composition of coating layer E Main material Oil Proto 100 Young's modulus (MPa) 12 Poison's ratio 0.495 Hardness (JIS-C) 43.5

The Oil Proto is a product name of a Hagitec product, which is produced of SBR resin as its main component. The detailed composition thereof includes gasoline (naphtha) of 33 to 37%, hexane of 13 to 16%, xylene of 15 to 19%, acetone of 8 to 10% and SBR resin of 24 to 28%.

In tests for measurement of the spin performance shown in Table 1, with a driver (Tour Stage X-Drive Type 455 9.5° manufactured by Bridgestone) and an approach wedge (Tour Stage X-WEDGE 58° manufactured by Bridgestone) mounted on a swing robot (manufactured by Miyamae), a golf ball was hit at a head speed of 45 m/s for the driver, and at a head speed of 25 m/s for the approach, and the ball just after it was hit was photographed with a high-speed camera to measure its spin amount (rpm).

In COR durability measurement test shown in Table 1, an ADC ball COR Durability Tester Machine manufactured by Automated Design Corporation in US was used to evaluate the durability of a golf ball. This tester machine has a function of shooting a golf ball with pneumatic pressure and striking it against two metallic sheets placed in parallel. An average of times of shoots required until the golf ball breaks is referred to as COR durability. In this case, the average value mentioned here refers to an average of the number of shoot times required until each of the prepared seven balls of the same type breaks after being shot. The tester machine type was a lateral COR type and an incident speed to the metallic sheet was 43 m/s.

As for the measurement method of Young's Modulus in Table 4, materials having each composition were formed into a sheet having a thickness of 2 mm and stored under an environment of 23±1° C. for two weeks. They were processed into a dumbbell-like No. 3 test pieces according to JIS K6251, and using Tensilon Universal Tester RTG-1310 manufactured by A&D, their tensile strengths (MPa) when the test piece was elongated by 10% were measured at a test speed of 500 mm/min. Then, their Young's Moduli were calculated from these measured tensile strengths. In the meantime, three test pieces were prepared for each composition and an average of those measured values was obtained to indicate its measurement result.

As shown in Table 1, the comparative examples 1 and 2 provided with no coating layer have a μ hardness of more than 3 and a hard cover structure. The comparative example 3 has a large product μ hardness. Thus, although these comparative examples ensured a predetermined performance in the spin amount for an approach, the spin amounts for a driver were very small.

On the other hand, in the examples 1 to 8, the coating layer formed of a material having rubber elasticity was arranged between the intermediate layer and the cover or between the core and the intermediate layer. As a result, a shock was absorbed by the coating layer and at the same time, the spin amount for a driver shot increased greatly without a large increase in the spin amount for approach. 

What is claimed is:
 1. A golf ball comprising: a core located in a center of the golf ball; a cover that surrounds an outside of the core and has a plurality of dimples on the surface thereof; and a coating layer located between the core and the cover, the coating layer being formed of a material having rubber elasticity.
 2. The golf ball according to claim 1, further comprising an intermediate layer located between the core and the cover, wherein the coating layer is located between the core and the intermediate layer or between the intermediate layer and the cover.
 3. The golf ball according to claim 1, wherein the golf ball has a μ hardness of at least 3.0, and wherein the cover has a hardness of at least approximately 50 in terms of Shore D hardness.
 4. The golf ball according to claim 2, wherein the intermediate layer has a hardness of approximately 40 to 65 in terms of Shore D hardness and the hardness of the cover is higher than the hardness of the intermediate layer.
 5. The golf ball according to claim 1, wherein the coating layer has a thickness of approximately 10 to approximately 150 μm.
 6. The golf ball according to claim 1, wherein a material used for forming the coating layer has a Young's modulus of approximately 70 MPa.
 7. The golf ball according to claim 1, wherein the material used for forming the coating layer has a Poisson's ratio of at least approximately 0.45.
 8. The golf ball according to claim 1, wherein the coating layer has a hardness of at most approximately 70 in terms of JIS-C hardness.
 9. The golf ball according to claim 1, wherein the cover comprises ionomer resin. 